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UNC Researchers Discover a New Understanding of Chronic Pain

Does chronic pain after trauma have a physiologic basis, or is it all in a patient’s head? UNC researchers have been looking at the physiology of chronic pain.

By Stephanie Soucheray

When a patient suffers a traumatic experience – a sexual assault or a car accident – many are likely to have acute pain immediately after the event. But for an unlucky 20 percent to 30 percent of patients, that acute pain turns into chronic pain.

Neuronal communication, image courtesy National Institute on Aging

“We have patients who complain of pain weeks after the event, and the pain is not necessarily connected to where they were injured during the traumatic event,” said Sam McLean, director of the UNC School of Medicine’s TRYUMPH Research Program and the Center for Neurosensory Disorders.

McLean said that these patients are often told dismissively that their pain is a psychological reaction to their trauma – that it’s “all in their head.” Even worse, McLean said some providers mistake their patient’s complaints months after a traumatic event as drug-seeking behavior, and are cautious when prescribing medication.

“We have a true epidemic of under-treated pain patients in this country,” McLean said. Because the stigma of mental illness and drug-seeking behavior follows anyone who walks into a doctor’s office complaining of pain, McLean said he’s trying to show that chronic pain after a traumatic event has a physical cause.

“If we can show the biology of this type of pain, we can reduce the stigma,” he said.

In a paper published on April 29 in the journal Pain , McLean and his colleagues describe how the pain sustained after a traumatic injury may have a genetic root.

A study that looked at patients for six weeks after a traumatic event showed that people with a variation in the gene encoding for the protein FKBP5 (which helps control the HPA Axis) were 20 percent more likely to experience chronic pain after a trauma.

The HPA Axis regulates cortisol and other stress hormones, and McLean said that the axis may be overly activated in some groups of people after they experience a traumatic event. This means musculoskeletal pain may be a result of a faulty stress response, and not any injury that occurred during the traumatic stress.

McLean described one study participant who was raped. The mother of two young children did not resist her assailant because she thought it would risk her life.

“Here was a woman with no bruises, no traumatic injury or tissue trauma to speak of, yet she had terrible chronic pain after the rape,” he said.

Although finding a genetic clue to such pain is exciting, McLean doesn’t want patients to get the wrong message about his research.

“I don’t want people to think, ‘Oh, I have these genes, now I’m hosed,’” said McLean. “We have just found an influential gene, and this guides us on future genetic studies and helps us develop the biological mechanisms that elucidate chronic pain.”

McLean said his research could lead to early interventions – for example, with a serotonin norepinephrine inhibitor (SNRI), or even mindfulness meditation. Moreover, he said the work could help bring light to the existence of post-traumatic pain disorders.

“In the last century, we accepted the idea of PTSD,” said McLean. “In the 21st century, we may begin to explain that chronic pain is a sequela of traumatic stress.”